The invention relates to a pyrodetector with a sharply limited directional range of detection sensitivity for the detection of a body entering into its detection directional range at a greater distance from the detector, the body having a temperature which deviates from that of its environment. Such a pyrodetector of the Heimann Company, Wiesbaden, for room supervision, for example, has a temperature-sensitive element situated at the focal point of a concave mirror. A window consisting of a germanium pane is situated in front of this sensor element. The window has a plurality of vapor deposition layers with which visible radiation and near infrared is filtered out. By so doing, the sensor element is only exposed to such longer wave infrared radiation as is persistently radiated from a living body.
Bolometers such as are described, for example, in U.S. Pat. No. 2,855,492, incorporated herein by reference, are known for another objective, namely for the quantitative measurement of the intensity of thermal radiation. Here again arrangements are shown with thermosensors which are likewise arranged in a concave mirror whose inside, in particular, is evacuated. In addition to the actual electrical resistance responding to the thermal irradiation, the arrangement disclosed in this Letters Patent also contains a second compensating resistor protected from the thermal irradiation. The compensation is carried out electrically with the assistance of a Wheatstone bridge.
A radiation meter disclosed in German Pat. No. 2,137,848, incorporated herein by reference, is known for yet another purpose. This radiation meter is intended for the remote display of the surface temperature of a test object arranged at a distance. This meter functions with two barretters, i.e. ceramic PTC--resistors, which must have differing Curie Temperatures, and whose characteristic curves which do not coincide must nonetheless exhibit the same steepness, at least in the measuring range. One of these barretters or PTC resistors is arranged in a focal point of the provided mirror. The other barretter is arranged in such manner that, in an additionally provided bridge circuit, it effects a compensation of the barretter quantitatively measuring the temperature, i.e. effects a zero offset compensation.